Machines are available for cutting hard surfaces such as concrete and asphalt. To cut such hard surfaces, a wheel is rotated about its axis and cutting tools mounted on the wheel are applied against the surface and each tool removes a small portion of hardened material thereby advancing the cut.
To maximize the useful life of such cutting tools, the tools are rotatably mounted about a longitudinal axis and have a cylindrical mounting portion rotatably fitted into a cylindrical aperture on a mounting block. Force is applied from the mounting block on the wheel against a rearward surface of an annular flange on the tool which rests upon a forward surface of the mounting block.
The body of the tool to which the tungsten carbide cutting tip is attached and the tool mounting block into which the cylindrical mounting portion of the tool is fitted are made of cold formed or forged steel which is much softer than the tungsten carbide cutting tip. As the machine cuts hard surfaces such as asphalt or concrete, fragments of the broken surface are forced across the tapered forward portion of the tool and around the forward and side portions of the mounting block causing wear or wash away of the material which makes up both the tool and the mounting block. After a substantial portion of the forward end of the tool has been worn away, the tool must be replaced. Similarly, after a substantial portion of the body of the mounting block has been washed away, the tool mounting block must also be replaced.
The rotation of the tool within the block occurs as a result of an uneven application of forces against the tool as it is applied to the hardened surface and, therefore, the mated annular surfaces on the block and on the tool, which transfer force from the block to the tool, also serves as a bearing surface for the rotation of the tool within the block. Over a period of use, particles of hardened material broken up by the tool work along the forward surface of the mounting block and under the rearward surface of the flange causing the mated surfaces to become irregular and thereby increasing the friction between the surfaces. The increased friction reduces the rotatability of the tool within the block. A tool which does not rotate within the mounting block will wear unevenly, thereby substantially reducing its useful life.
In recent years, the annular flanges behind the forward cutting ends of tools have been made larger in diameter to provide additional protection to the mounting block such that the body of the mounting block will remain intact much longer than the body of the tool retained therein. Although the presence of the enlarged flange on such tools has served to protect the body of such mounting blocks against wash away, the particles of hardened material nonetheless work their way between the abutting surfaces of the mounting block and the tool and cause the forward surfaces of the mounting block and the surface of the cylindrical aperture extending through the mounting block to become worn. As a result of the wear on these two surfaces, a replacement tool inserted in the mounting block will not be snugly retained in the aperture, nor will the replacement tool rotate freely therein. As a result of the foregoing, when a tool is inserted into a previously used mounting block, the replacement tool frequently has a useful life which is much shorter than that of the original tool.
It would be desirable, therefore, to provide a mounting block for which the critical surfaces required to rotatably retain a tool therein will not become so worn as to be unusable during the useful life of a single tool.